By Marion Lloyd,
IRANDUBA, Brazil -- High along bluffs overlooking the confluence of the mighty Negro and Solomes rivers, super-sized eggplants, papayas and cassava spring from the ground.
Their exuberance defies a long-held belief about the Amazon. For much of the last half-century, archeologists have viewed the South American rain forest as a ''counterfeit paradise" whose inhospitable environment precluded the development of complex societies.
But new research suggests that prehistoric people found ways to overcome the jungle's natural limitations and thrive in large numbers.
The secret, say the theory's proponents, is in the ground beneath their feet. The highly fertile soil called terra preta do indio, Portuguese for Indian black earth, was either intentionally created by these pre-Columbian people or is the accidental byproduct of their presence.
The research has implications not only for history but for the future of the Amazon rain forest. If scientists could discover how the Amerindians transformed the soil, farmers could use the technology to maximize the productivity of smaller plots of land, rather than cutting down ever larger swaths of jungle. The benefits of this ''gift from the past" are already known to farmers in the area, who plant their crops wherever they find terra preta.

''It's made by pre-Columbian Indians and it's still fertile," said Bruno Glaser, a soil chemist from the University of Bayreuth in Germany who took samples of terra preta recently near the jungle town of Iranduba. ''If we knew how to do this, it would be a model for agriculture in the whole region."
This specially modified soil is scattered across millions of acres in the Amazon rain forest, in some areas comprising 10 percent of the ground area. And it is typically packed with potsherds and other signs of human habitation.
''We believe there weren't just tribal societies here, but rather complex chiefdoms, and we're providing the proof," said James B. Petersen, an archeologist from the University of Vermont who has spent the past decade working in the Brazilian Amazon. His team of American and Brazilian archeologists, who call themselves the Central Amazon Project, have excavated more than 60 sites rich in terra preta near the jungle city of Manaus, where the Negro and Solomes rivers merge to form the Amazon River proper.
On some of the sites, several square miles of earth are packed with millions of potsherds. The archeologists also cite evidence of giant plazas, bridges and roads, complete with curbs, and defensive ditches that would have taken armies of workers to construct.
The earliest signs of large, sedentary populations appear to coincide with the beginnings of terra preta. ''Something happened 2,500 years ago, and we don't know what," said Eduardo Neves, a Brazilian archeologist at the Federal University of So Paulo, who is codirector of the Central Amazon Project.